wireless sensor network dr. monir hossen ece, kuet department of electronics and communication...
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Wireless Sensor Network
Dr. Monir HossenECE, KUET
Department of Electronics and Communication Engineering, KUET
Department of Electronics and Communication Engineering, KUET 2
Introduction Differences with ad hoc networks Applications Characteristics Challenges Future Motes Hardware Setup Overview
Agendas of This Lecture
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Introduction Wireless Sensor Networks (WSNs) are networks that consists
of sensor nodes which are distributed in an ad hoc manner WSN consisting of spatially distributed autonomous devices
using sensors to cooperatively monitor physical or environmental conditions:
- Temperature - Sound - Pressure - Home automation - Traffic control - Healthcare application
Main Devices of WSN
Sensor Nodes and PANC
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Characteristics of Wireless Sensor Networks
Wireless Sensor Networks mainly consists of sensor nodes. Sensor nodes are -o Low power deviceo Consist of limited memoryo Energy constrained due to their small size.
Wireless networks can also be deployed in extreme environmental conditions and may be prone to enemy attacks.
Although deployed in an ad hoc manner they need to be self organized and self healing and can face constant reconfiguration.
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Design Challenges of WSN (1/2)
Heterogeneity => The devices deployed maybe of various types
and need to collaborate with each other.
Distributed Processing=> The algorithms need to be centralized as the
processing is carried out on different nodes.
Low Bandwidth Communication=> The data should be transferred efficiently
between sensor nodes.
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Design Challenges of WSN (2/2) Large Scale Coordination
=> The sensors need to coordinate with each other to produce required results.
Utilization of Sensors=> The sensors should be utilized in a ways that
produce the maximum performance and use less energy.
Real Time Computation=> The computation should be done quickly as
new data is always being generated.
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Operational Challenges of WSNs Energy Efficiency Limited storage and computation Low bandwidth and high error rates Errors are common
Wireless communication Noisy measurements Node failure are expected
Scalability to a large number of sensor nodes
Survivability in harsh environments Experiments are time- and space-
intensive
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The Growth of Sensor Networks WSNs grown from simple point-to-point networks with simple interface protocols providing sensing and control informationThe sensor node has increased onboard intelligence and processing capabilities thus providing it with different computing capabilities The development of the Manufacturing Automation Protocol (MAP), reduced the cost of integrating various networking schemes into a plant wide system The development of other communication protocols allowed simultaneous analog and digital communications created a sensor network
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Enabling Technologies
Embedded
Control system w/Small form factorUntethered nodes
Networked
Exploitcollaborative
Sensing, action
Sensing
Tightly coupled to physical world
Embed numerous distributed devices to monitor and interact
with physical world
Network devices to coordinate and perform higher-level tasks
Exploit spatially and temporally dense, in situation of sensing and actuation
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Future of WSNSmart Home / Smart Office
Sensor nodes controlling appliances and electrical devices in the house.
Better lighting and heating in office buildings.
The Pentagon building has used sensors extensively.
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Biomedical / Medical Health Monitors
Glucose Heart rate Cancer detection
Chronic Diseases Artificial retina Cochlear implants
Hospital Sensors Monitor vital signs Record
irregularities
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Military
Remote deployment of sensors for tactical monitoring of enemy troop movements.
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Industrial & Commercial
Numerous industrial and commercial applications:o Agricultural Crop Conditionso Inventory Trackingo In-Process Parts Trackingo Automated Problem Reportingo RFID – Theft Deterrent and Customer
Tracingo Plant Equipment Maintenance Monitoring
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Traffic Management & Monitoring Future cars could use
wireless sensors to:Handle AccidentsHandle Thefts
Sensors embedded in the roads to:=> Monitor traffic flows=> Provide real-time route
updates=> Monitor the speed of a
car
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Typical Multi-hop WSN Architecture
PANC
Sensor Node
Since area of u-City is increasing: Diameter of WSN is
increased (> 10 Km)
Number of sensor nodes are increased ( > multi-decades of thousands)
Number of wireless hopes are increased (>15)
Reverse time delay is increased
WSN Normally Constitutes an Multi-hop Wireless Network
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Limitations of Multi-hop WSNs
The Multi-hop WSN Possess the Following Limitations:
- Large Time Delay
- Huge Traffic Overcrowding
- Data Repetition Multiple Times
- Huge Energy Loss
- Difficult to Protect The Failure of a Node
- Large Time for Fault Analysis
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Data Transmission Protocol in WSN
PNC Sensor Node 1
Beacon
Data
Acknowledgment
Beacon
Beacon
Data
DataAcknowledgmentAcknowledgment
Sensor Node 4
Sensor Node 2
Sensor Node 3
Beacon
Data
Acknowledgment
(optional)
(optional)
(optional)
(optional)
Two Types of Data Transaction Exist:
- PANC Sensor Node
- Sensor Nodes PANC
DS
US
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Routing Protocols in WSNs
Hierarchical-Based
Location-Based
Flat-Based
Routing Protocols
Traditional Routing Current Routing
Flooding Gossiping
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Flooding Protocol A classical mechanisms to relay data in sensor
networks without the need for any routing algorithms and topology maintenance. It broadcasts data.
Drawbacks:• Implosion (duplicate packet
may receive)• Overlap (two sensors send
a packet and at the same time) • Resource blindness (without checking node’s
status it transmits packets)
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Gossiping Protocol A slightly enhanced version
of flooding where the transmitting node sends the packet to a randomly selected neighbor which picks another neighbor to forward the packet to and so on. Advantage: avoid the
collapse Drawback:
Transmission delay
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Flat-Based Routing Protocols (1/2) All the nodes are treated equally and have the
same functionality
1. Sensor Protocol for Information Negotiation (SPIN): Sending meta -data to neighboring nodes, instead of data Requesting for the desired data
Avoid redundant data transmission Adaptation to remaining energy increase network
lifetime
2. Directed Diffusion: BS continuously sends query to the neighboring nodes Node with the desired data transmit all the way back to BS
Saving energy by selecting the optimal return path Not practical for continuous data demand cases
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Flat-Based Routing Protocols (2/2) 3. Rumor Routing:
Variation of Directed Diffusion Each node has an event table Event agent flooding instead of query flooding
Significant energy saving Good for when number of events is less than queries
4. Minimum Cost Forwarding Algorithm (MCFA): Each node knows the least cost path between itself and BS Least cost path can be acquired via initialization
Saving energy by selecting the optimal return path Good for small networks
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Hierarchical Routing (1/3) Higher energy nodes for transmission, lower
energy nodes for sensing Two layer routing Increasing the life time
1. Low Energy Adaptive Clustering Hierarchy (LEACH): Random and variation Cluster Head (CH) selection Compression and transmission of arriving data at CHs
Constant monitoring applications Good for small networks Extra overhead because of clustering
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Hierarchical Routing (2/3)
2. Self Organizing Protocol (SOP): Mobile sensors to probe the environment Stationary nodes as the routers LML algorithm for routing Energy consumption is less than SPIN
3. Virtual Grid Architecture Symmetric, non-overlapping clusters with optimal CH Local and global data aggregation
Hard to find the optimal global aggregators
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Hierarchical Routing (3/3)
4. Hierarchical power-aware routing Proximate nodes form zones Routes through the zones
which has maximum minimum residual energy Extra algorithm can be
exploited
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Location-Based Routing o Sensor nodes are addressed based on their locationo Location are acquired by GPS or via coordination
among nodes1. Geographical Adaptive Fidelity (GAF):
Network divided into zones Only one node is awake in each zone, the rest sleep
Conserves energy by turning off unnecessary nodes Increases the network life time
2. SPAN: Some nodes are selected as coordinators based on their
positions Enough coordinators such that network is three-hop
reachable Not energy efficient as the others
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Routing Protocols Based on Protocol Operation
1. Multipath routing Increases fault tolerance Sophisticated case: have back up paths
2. Query-based routing Query transmitted and the date is sent back
3. Negotiation-based routing High-level data description Elimination of redundant data transmission
4. QoS-based routing Balance between data quality and energy consumption
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Hidden Terminal Problem
A
BC
Hidden terminalsA and C cannot hear each other.A sends to B, C cannot receive A. C wants to send to B, C senses a “free” medium (CS fails)Collision occurs at B.A cannot receive the collision (CD fails).A is “hidden” for C.
Solution?Hidden terminal is peculiar to wireless (not found in wired)Need to sense carrier at receiver, not sender!“virtual carrier sensing”: Sender “asks” receiver whether it can hear something. If so, behave as if channel busy.
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Exposed Node Problem Exposed node problem occurs when a node is prevented
from sending packets to other nodes due to a neighboring transmitter.
If a transmission between S1 and R1 is taking place, node S2 is prevented from transmitting to R2 as it will interfere with the transmission by its neighbor S1
However note that R2 could still receive the transmission of S2 without interference because it is out of range of S1
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IEEE 802.11 MAC Protocol: CSMA/CA
802.11 CSMA: SenderIf sense channel idle for DIFS (Distributed Inter Frame Space) then transmit entire frame (no collision detection)If sense channel busythen binary back off
802.11 CSMA: ReceiverIf received OKreturn ACK after SIFS --Short IFS (ACK is needed due to hidden terminal problem)
NAV: network allocation vector
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Collision Avoidance Mechanisms
Problem: Two nodes, hidden from each other, transmit complete frames to base stationWasted bandwidth for long duration!
Solution: Small reservation packets: RTS+CTSNodes track reservation interval with internal (NAV)
Thanks for Your Kind Attention
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